During the first division of the embryo forming a two-cell stage, PIN 7 is localized to the top plasma membrane of the basal cell, inducing the transport of auxin from the adjacent basal cell to the top cell, in which auxin accumulates. At the spherical embryo stage, PIN 1 appears at the basal plasma membrane of the cell, meanwhile, PIN 7 turns to the basal plasma membrane of basal cells and PIN 4 begins to be expressed at the base of the embryo, thus inducing auxin transport from the embryonic cell to the radicagen and promoting radicagen development.
